We aim at investigating the molecular mechanisms of hyperglycemia-induced dysfunction of the endogenous antioxidant system of the thioredoxins (TrxS) in the diabetic retina. Our overall goal is to identify ways to rescue the activity of this critical regulator of cellular redox homeostasis in diabetes mellitus, thereby, preventing hyperglycemia-induced oxidative stress (OxS) and chronic inflammatory processes. To date, hyperglycemia-induced loss of TrxS function has been attributed only to increased expression of the thioredoxin interacting protein (TXNIP). However, in streptozotocin-induced diabetic rats (STZ-rats) and human diabetic retinas, we have discovered that hyperglycemia promotes serine phosphorylation of TXNIP (TXNIP- SerP), nitration/inactivation of the thioredoxin reductase 1(TrxR1-NY) and deacetylation of thioredoxin 1(Trx1). These modifications are associated with decreased bioavailability of the reduced (active) form of Trx1, the operating unit of the system, and with TXNIP gain of function. We have also determined that TXNIP and Trx1 post-translational modifications, involve the activity of protein kinase C delta (PKC?) and histone deacetylase 6 (HDAC6), respectively, implicating for the first time HDAC6 in the pathogenesis of DR and disclosing a new function of PKC? in the diabetic retina. We have designed experiments aimed at validating our hypothesis that: in the diabetic retina, impaired function of TrxS results from TXNIP serine phosphorylation, TrxR1 nitration/ inactivation and Trx1 deacetylation. These modifications of the TrxS constituents will lead to impaired antioxidant ability, induction of inflammatory processes and progression to DR. We have designed experiments to be conducted in vitro on isolated retinal pericytes (RPC) and endothelial cells (REC) exposed to elevated glucose levels (HG) and osmotic controls. In vivo experiments will be conducted by using streptozotocin-induced diabetic rats (STZ-rats, a model of Type1 diabetes). Aim1. Test the hypothesis that PKC?-dependent TXNIP-SerP contributes to retinal OxS, inflammation and progression to DR. Aim2. Test the hypothesis that TrxR1-NY contributes to retinal OxS and progression to DR. Aim3. Test the hypothesis that HDAC6-mediated de-acetylation of Trx1 contributes to retinal OxS, inflammation and progression to DR.